The microblogging service will continue to invest and hire in Japan and will also add engineers, Costolo said Monday in Tokyo without specifying investment amounts or the number of people being added.

Twitter, which lets users post 140-character messages, is expanding abroad to decrease its reliance on the U.S. market. The percentage of revenue that Twitter earns from the U.S. will fall to 83 percent in 2014 from about 90 percent this year, researcher EMarketer estimated in January. Japan had the third-largest share of Twitter users with 29.9 million accounts created before Jan. 1, according to Semiocast, a social media research company.